Most refrigeration and heat pump devices operate on a thermal cycle which requires the compression of a refrigerant gas such as R22 freon, although other gases are also in common use in compression refrigeration cycles. In such devices and refrigeration methods, it is well recognized that efficiency and COP are enhanced when the vaporized refrigerant is compressed in stages and the liquid refrigerant is expanded in stages. Because of the uneconomical increases in the size of compressing equipment, the practice of using a dual or multiple compression cycle has not become common. In such devices the low suction pressure gas is admitted to a first stage cylinder. When elevated to intermediate stage pressure the gas or a portion thereof is admitted to a second stage of cylinders wherein the pressure of the gas is raised again. At the end of the second stage it may be at the proper condition for admission to the condenser, or it may be pre-cooled, before expansion into the condenser. In certain circumstances, in some instances, further stages are added.
Reduction in the size of two stage refrigerant compression systems is known to be possible by also accomplishing the expansion of the liquid in two stages. The first expansion is from condenser pressure to the intermediate pressure where a chamber allows the expanded vapor to be separated into its liquid and vapor portions. The liquid is expanded to evaporator pressure and the reduced mass flow of vapor entering the first compression stage from the evaporator reduces the physical size requirements of the compressor. The vapor separated from the liquid expansion at interstage pressure joins the vapor discharge from the first compression stage as a combined inlet to the second compression stage. Further reductions in compressor size are known to be possible by injecting the separated vapor at intermediate pressure into a single stage compressor after the low pressure inlet is completed.
As a matter of convenience the term "dual compression systems" will be used herein, it being understood that more than two stage systems should be included in the concepts where appropriate.
In some systems and apparatus, a plurality of pistons and cylinders operate separately and are interconnected to a common, or a plurality of, crankshafts which are turned by a power source.
Rotary compressors are commonly used, with conduits interconnecting the compression chambers, with appropriate check valves, etc.
U.S. Pat. No. 3,139,835 Wilkinson, by the same inventor as of this invention, reveals a gear teeth-like rotary pump in which rotatable elements provide a plurality of fluid compartments of continuously varying dimensions. The device is described as a compressor when it is used to pump a compressible fluid. Compressed fluid is ejected from the compartments through ports into an encircling member containing a distribution duct. The distribution duct passes the first stage compressed fluid from the discharge ports of the first stage compression compartments to a plurality of second stage compression compartments.
In the patent, the number of "gear" teeth is one less than the number of fluid compression compartments and the number of compression compartments is one less than the number of port sets in the manifold which surround the exterior of the fluid compartment ring. These compression compartments are influenced and controlled by the eccentricity of the drive shaft relative to the center of the drive planet pinion, which is rotating in the driven planetary ring gear.
In the operation of that device, there is a "vernier" effect between the ports and the manifold chambers so that with each revolution of the compression compartment ring, a port in each compartment connects with a successive manifold chamber on the internal periphery of the port ring, and the external periphery of the compression chamber ring. This vernier effect makes it possible to equalize the port pressure at the time of opening of the discharge ports from the compression chambers in the device, even though the device has a greater number of compression chambers than gear teeth on the internal compressor gear. More importantly, the vernier action reduces the relative velocity between the port ring and the compression compartment ring to reduce the friction drag at the clearances necessary to limit leakage.
U.S. Pat. No. 3,157,024 to McCrory and Wilkinson, the latter being the same inventor as of this invention, discloses a crossed piston device operated with an open regenerative thermal cycle (Ericcson). The crossed piston device operates by means of an eccentrically positioned crank bearing on a crankshaft to move a pair of oppositely disposed pistons rotatively connected to the bearing of the crankshaft. The pistons reciprocate in a cylinder block which may be rotatively disposed in an encircling port or manifold ring. As seen in FIGS. 22 and 23 the number of port positions is less, relative to the number of pistons, there being four in the examples shown. As shown, there are three port positions and four piston cylinder combinations.
In this patent a vernier effect is provided for the purpose of controlling the working fluid flow between the pairs of cylinders that accomplish the sequential open cycle process.
The principles of operation of the cross cylinder device are shown in FIGS. 1-5 and 6-9 of the reference patent, as described in Columns 3 beginning at Lines 44 and through Column 4, Line 47. The description therein is included herein by reference for understanding of the invention to be described in this disclosure.
U.S. Pat. No. 4,332,144 Shaw discusses the advantages of utilizing a scavenge vapor generator or recovery heat exchanger as a means of increasing the coefficient of performance in vapor compression closed loop refrigeration and heat pump systems, through staging the expansion of the liquid refrigerant. In that device the higher pressure scavenge refrigerant enters the interior of the compression chamber as vapor through ports that are opened near the bottom dead center position of the piston so that the same piston stroke is subdivided so as to accomplish a two-stage effect without the added size of two separate compression stages. This patent is a typical example of prior art endeavors to increase the efficiency of the compressor and the system by properly timing the admission of higher pressure gas without excessive displacement increases.